BIOLOGY AND PATHOLOGY OF A SPECIES OF PHAEORAMULARIA CAUSING A LEAF-SPOT OF CROFTON WEED

The identity, biology and pathology of a Phaeoramularia sp. isolated f rom crofton weed, Ageratina adenophora, were investigated to assess it s potential as a mycoherbicide for control of crofton weed. Leaf infec tion by A. adenophora by a conidial suspension of Phaeoramularia sp. w as studied using light and electron microscopy. Under optimum conditio ns, Phaeoramularia sp. could penetrate leaves via stomata 5 days after inoculation and express leaf-spot symptoms and produce conidiophores on the leaf surface within 7 days. An investigation of various host an d environmental factors showed that the optimum conditions for infecti on of seedlings of crofton weed with Phaeoramularia sp. were an inocul um concentration of 10(6) conidia/mL, a dew period of at least 18 h an d a temperature of 19 to 24 degrees C during and after the dew period. The use of Phaeoramularia sp. as a mycoherbicide on A. adenophora has some potential if high inoculum concentrations are used and young pla nts are sprayed in moist warm conditions.